WO2024084018A1 - Produit plat en acier permettant de produire une pièce en acier par formage à chaud, son procédé de production et procédé de production de pièce en acier - Google Patents

Produit plat en acier permettant de produire une pièce en acier par formage à chaud, son procédé de production et procédé de production de pièce en acier Download PDF

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Publication number
WO2024084018A1
WO2024084018A1 PCT/EP2023/079226 EP2023079226W WO2024084018A1 WO 2024084018 A1 WO2024084018 A1 WO 2024084018A1 EP 2023079226 W EP2023079226 W EP 2023079226W WO 2024084018 A1 WO2024084018 A1 WO 2024084018A1
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Prior art keywords
flat steel
steel product
carbon particles
temperature
aqueous dispersion
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PCT/EP2023/079226
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German (de)
English (en)
Inventor
Robin Dohr
Michael Stang
Maria KÖYER
Christian Altgassen
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Thyssenkrupp Steel Europe Ag
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Publication of WO2024084018A1 publication Critical patent/WO2024084018A1/fr

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Classifications

    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/04—Ferrous alloys, e.g. steel alloys containing manganese
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B32—LAYERED PRODUCTS
    • B32B—LAYERED PRODUCTS, i.e. PRODUCTS BUILT-UP OF STRATA OF FLAT OR NON-FLAT, e.g. CELLULAR OR HONEYCOMB, FORM
    • B32B15/00—Layered products comprising a layer of metal
    • B32B15/01—Layered products comprising a layer of metal all layers being exclusively metallic
    • B32B15/012—Layered products comprising a layer of metal all layers being exclusively metallic one layer being formed of an iron alloy or steel, another layer being formed of aluminium or an aluminium alloy
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C21/00—Alloys based on aluminium
    • C22C21/02—Alloys based on aluminium with silicon as the next major constituent
    • C22C21/04—Modified aluminium-silicon alloys
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/06—Ferrous alloys, e.g. steel alloys containing aluminium
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
    • C22C38/32—Ferrous alloys, e.g. steel alloys containing chromium with boron
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
    • C22C38/28—Ferrous alloys, e.g. steel alloys containing chromium with titanium or zirconium
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
    • C22C38/38—Ferrous alloys, e.g. steel alloys containing chromium with more than 1.5% by weight of manganese
    • C—CHEMISTRY; METALLURGY
    • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
    • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
    • C23C30/00—Coating with metallic material characterised only by the composition of the metallic material, i.e. not characterised by the coating process

Definitions

  • the invention relates to a flat steel product for producing a steel component by hot forming, a method for producing such a flat steel product, a method for producing a sheet metal part from such a flat steel product and the use of carbon particles in an absorption layer on a flat steel product coated with an aluminum-based anti-corrosion coating for reducing the reflectivity in the infrared range.
  • flat steel product refers to all rolled products whose length is several times greater than their thickness. This includes steel strips and sheets as well as cut pieces and blanks made from them.
  • hot forming also known as hot forming, press hardening or hot press hardening
  • flat steel products such as steel blanks, which are cut from cold or hot rolled steel strip
  • AC3 austenitizing temperature
  • the sheet metal blank or the component formed from it undergoes rapid cooling due to contact with the cool tool.
  • the cooling rates are set so that a hardened structure is created in the steel substrate.
  • the structure is converted into an at least partially martensitic structure.
  • hot forming produces a hardened steel component.
  • the heating of the flat steel product is typically carried out in a preheated roller hearth furnace through which the flat steel product passes.
  • this results in the problem that the radiant heat is reflected on the smooth and reflective surfaces of the metallic anti-corrosion coating applied to the flat steel product. This leads to a significant delay in the heating process, with the result that more time and energy is required for the heating.
  • a shortened heating time of the flat steel product to the deformation temperature would mean that the corresponding roller hearth furnaces could be dimensioned shorter, which would have a positive effect on both the space required and the cost of purchasing them.
  • a shortened heating time could reduce the duration of the process.
  • the CO2 emissions generated during the process could also be reduced. Overall, this would result in an optimized process control option.
  • the object underlying the invention was to provide a flat steel product that can be heated to the initial temperature required for hot forming within shorter heating times.
  • a process that The invention also aims to provide a method for producing a sheet metal part made from such a flat steel product.
  • a flat steel product for producing a steel component by hot forming comprising a steel substrate consisting of a steel having 0.1-3 wt.% Mn and optionally up to 0.01 wt.% B, and an aluminum-based anti-corrosion coating applied to the steel substrate, wherein an absorption layer comprising carbon particles is arranged on the anti-corrosion coating.
  • carbon particles are particles made of elemental carbon.
  • Particles in the sense of the invention consist of a solid and have a hydrodynamic diameter of 1 to 500 nm.
  • Several of these primary particles can be connected to form aggregates with a hydrodynamic diameter of 50 to 1000 nm.
  • these aggregates are combined to form further agglomerates with diameters of 1 to 100 pm.
  • the hydrodynamic diameter of the particles is determined by means of dynamic light scattering (DLS).
  • the carbon particles are preferably those selected from the group consisting of graphite, fullerenes, graphene, carbon nanotubes and mixtures thereof.
  • Carbon particles have the advantage that even small amounts in the absorption layer result in significant absorption in the infrared range, and thus a reduction in reflectivity in the infrared range.
  • the infrared range is the area of the radiation spectrum in which the interior of the furnace emits radiation, which essentially serves to heat the sheet metal blanks to the forming temperature.
  • the reduction in the reflectivity of the flat steel product or the increase in absorption in the infrared range by the The absorption layer comprising carbon particles thus leads to a faster heating of the flat steel product to the forming temperature.
  • the absorption layer comprising carbon particles is almost completely burned during hot forming at 920°C, so that the absorption layer does not have a detrimental effect on the properties, such as weldability, corrosion tendency, scaling protection and paintability, of the sheet metal part obtained from the flat steel product after hot forming.
  • the infrared range is understood to mean the wave number range from 667 to 10,000 cm' 1. This corresponds to the wavelength range from 1 to 15 pm.
  • a well-adhering absorption layer with carbon particles can be easily created by immersing the flat steel product in an aqueous dispersion containing carbon particles or spraying it with such a dispersion or coating it using a coil coating process or chemical or physical gas deposition (CVD or PVD).
  • CVD chemical or physical gas deposition
  • an absorption layer with carbon particles is formed on the aluminum-containing surface of the anti-corrosive coating, which covers the highly reflective aluminum-based anti-corrosive coating.
  • the absorption layer lies on the anti-corrosive coating and is directly adjacent to it.
  • the absorption layer is a covering layer which closes off the layer structure formed on the flat steel product according to the invention on each of its outer sides.
  • the absorption layer has an application weight (dry) of 0.09 to 10 g/m 2 , in particular 0.5 to 5 g/m 2 , per side of the flat steel product.
  • Application weights of less than 0.09 g/m 2 do not show a sufficient reduction in the degree of absorption, while at application weights of more than 10 g/m 2 , especially more than 5 g/m 2 , the effect is saturated. Applying a higher application weight is therefore possible but uneconomical.
  • the thickness of the absorption layer is 0.05 to 5 pm.
  • the thickness is to be understood as the thickness per side of the flat steel product.
  • the two sides of the flat steel product are the two large surfaces of the flat steel product that are opposite each other. The narrow surfaces are referred to as edges.
  • the thickness on each of the two sides is therefore 0.05 to 5 pm. It has been shown that even such small thicknesses of the absorption layer lead to a significant reduction in the degree of reflection.
  • the reflectance R in the infrared range is determined in the sense of this application by using a black body radiator as a reference.
  • the spectral radiation power i z (T) of the black body radiator at the temperature T is therefore multiplied by the measured spectral reflectivity p . and integrated over the wavelength range. This integral is standardized to the spectral radiation power integrated over the same wavelength range. The following therefore applies:
  • i z (T) results from Planck's radiation law with the speed of light c, Planck's constant h and Boltzmann's constant kB.
  • the reflectance R used below is defined as R (920°C).
  • the absorption layer comprises carbon particles.
  • the proportion of carbon particles in the dry absorption layer can be 10-99% by weight, preferably 30-99% by weight, particularly preferably 50-99% by weight.
  • the effect according to the invention occurs even with very small amounts of carbon particles in the absorption layer and increases with increasing amounts of carbon particles.
  • a particularly high absorption in the infrared range, and thus a particularly advantageous reduction in reflectivity in the infrared range, is achieved when the proportion of carbon particles in the dry absorption layer is 60-99% by weight, in particular 80-99% by weight, preferably 90-99% by weight and particularly preferably 95-99% by weight.
  • the absorption layer has at least one surfactant.
  • the presence of the at least one surfactant leads to improved wettability of the absorption layer on the corrosion protection coating.
  • Suitable surfactants include anionic, cationic, zwitterionic and non-ionic surfactants as well as mixtures thereof.
  • the at least one surfactant is selected from the group consisting of alkyl sulfates, alkyl sulfonates, alkyl phosphonates, alkoxylated fatty alcohols, alkoxylated fatty acids, alkoxylated fatty acid amines, alkoxylated alkylphenols, or alkyl polyglycosides.
  • alkyl of the aforementioned alkyl sulfates, alkyl sulfonates, alkyl phosphonates, alkylphenols and/or alkyl polyglycosides has a chain length of 8 to 22 carbon atoms.
  • the alkoxylated fatty alcohols, fatty acids, fatty acid amines and/or alkylphenols can be ethoxylated, propoxylated or butoxylated fatty alcohols, fatty acids, fatty acid amines and/or alkylphenols.
  • the degree of ethoxylation, propoxylation or butoxylation can be from 1-18, preferably from 3-10.
  • the proportion of at least one surfactant in the dry absorption layer is 0.01 to 5 wt.%, in particular 0.5 to 2 wt.%.
  • a minimum content of 0.01 wt.% has proven to be necessary to ensure the wettability of the aluminum-based anti-corrosive coating.
  • a proportion of more than 5 wt.% surfactant in the absorption layer does not lead to any further improvement in wettability and is therefore not sensible from an economic point of view.
  • the absorption layer can also contain at least one polymer in addition to the surfactant.
  • An embodiment of the flat steel product according to the invention with an absorption layer comprising at least one surfactant and at least one polymer is therefore particularly preferred.
  • Suitable polymers include polyalkylene glycols and their mixtures.
  • the at least one polymer is selected from polyethylene glycols or polypropylene glycols. Good results can be achieved in particular with polyethylene glycols or polypropylene glycols whose molecular weight is in the range from 400 to 5000 g/mol.
  • the proportion of the at least one polymer in the dry absorption layer can be 1 to 90% by weight. A minimum content of 1% by weight is required to obtain the advantageous adhesion improvement mentioned. The addition of more than 90% by weight has a detrimental effect on the degree of reflection and the drying of the coating.
  • the aluminum-based anti-corrosive coating can be applied to one or both sides of the flat steel product.
  • "Aluminum-based anti-corrosive coating” as used here means that the anti-corrosive coating consists of more than 50% aluminum by weight.
  • Such a corrosion protection coating is preferably produced by hot-dip coating the flat steel product.
  • the flat steel product is passed through a liquid melt which consists of up to 15% by weight of Si, preferably more than 1% by weight, in particular more than 1.0% by weight of Si, optionally 2 to 4% by weight of Fe, optionally up to 5% by weight of alkali or alkaline earth metals, preferably up to 1.0% by weight of alkali or alkaline earth metals, and optionally up to 15% by weight of Zn, preferably up to 10% by weight of Zn and optionally further components, the total contents of which are limited to a maximum of 2.0% by weight, and the remainder being aluminum.
  • the Si content of the melt is 1 - 3.5 wt.% or 7 - 12 wt.%, in particular 8 - 10 wt.%.
  • the optional content of alkali or alkaline earth metals in the melt comprises 0.1 - 1.0 wt.% Mg, in particular 0.1 - 0.7 wt.% Mg, preferably 0.1 - 0.5 wt.%.
  • the optional content of alkali or alkaline earth metals in the melt can comprise in particular at least 0.0015 wt.% Ca, preferably at least 0.01 wt.% Ca.
  • the alloy layer lies on the steel substrate and is directly adjacent to it.
  • the alloy layer is essentially made of aluminum and iron.
  • the other elements from the steel substrate or the composition of the melt do not accumulate significantly in the alloy layer.
  • the alloy layer preferably consists of 35 - 60 wt.% Fe, preferably a-iron, optional further components, the total contents of which are limited to a maximum of 5.0 wt.%, preferably 2.0 wt.%, and the remainder aluminum, with the Al content preferably increasing towards the surface.
  • the optional further components include in particular the other components of the melt (i.e. silicon and optionally alkali or alkaline earth metals, in particular Mg or Ca) and the remaining parts of the steel substrate in addition to iron.
  • the Al base layer lies on the alloy layer and is directly adjacent to it.
  • the composition of the Al base layer preferably corresponds to the composition of the melt of the melt bath. This means that it consists of 1- 15 wt.%, in particular 1.0 - 15 wt.%, Si, optionally 2 - 4 wt.% Fe, optionally
  • alkali or alkaline earth metals preferably up to 1.0 wt.% alkali or alkaline earth metals, optionally up to 15 wt.% Zn and optional further components, the total contents of which are limited to a maximum of 2.0 wt.%, and the remainder aluminium.
  • the optional content of alkali or alkaline earth metals comprises 0.1 - 1.0 wt.% Mg, in particular 0.1 - 0.7 wt.% Mg, preferably 0.1 - 0.5 wt.% Mg.
  • the optional content of alkali or alkaline earth metals in the Al base layer can comprise in particular at least 0.0015 wt.% Ca, in particular at least 0.1 wt.% Ca.
  • the Si content in the alloy layer is lower than the Si content in the Al base layer.
  • the anti-corrosive coating preferably has a thickness of 5 - 60 pm, in particular 10 - 40 pm.
  • the coating weight of the anti-corrosive coating is in particular 30 - 360 g/m 2 for anti-corrosive coatings on both sides or 15 - 180 g/m 2 for the one-sided variant.
  • the coating weight of the anti-corrosive coating is preferably 100 - 200 g/m 2 for coatings on both sides or 50 - 100 g/m 2 for coatings on one side.
  • the coating weight of the anti-corrosive coating is particularly preferably 120 - 180 g/m 2 for coatings on both sides or 60 - 90 g/m 2 for coatings on one side.
  • the thickness of the alloy layer is preferably less than 20 pm, particularly preferably less than 16 pm, particularly preferably less than 12 pm, in particular less than 10 pm.
  • the thickness of the Al base layer results from the difference between the thicknesses of the anti-corrosive coating and the alloy layer.
  • the thickness of the Al base layer is preferably at least 1 pm, even with thin anti-corrosive coatings.
  • the average reflectance R in the infrared range is less than 0.55, in particular less than 0.50, preferably less than 0.45, in particular less than 0.40, preferably less than 0.35, particularly preferably less than 0.30, in particular less than 0.25, preferably less than 0.20, in particular less than 0.15. The smaller the reflectance in the infrared range, the higher the heating rate during the subsequent production of a steel component.
  • the invention also relates to the use of carbon particles in an absorption layer on a flat steel product coated with an aluminum-based anti-corrosion coating to reduce reflectivity in the infrared range.
  • the use has the same advantages as explained above with respect to the flat steel product.
  • the invention also relates to the use of the above-mentioned specially developed absorption layers and in particular to the use of a mixture of carbon particles with at least one surfactant and/or polymer in an absorption layer on an anti-corrosion coating with 0.1 - 1.0 wt.% Mg in the Al base layer.
  • the steel substrate is made of a steel that contains 0.1 - 3 wt.% Mn and optionally up to 0.01 wt.% B.
  • the structure of the steel can be converted into a martensitic or partially martensitic structure by hot forming.
  • the structure of the steel substrate of the steel component is therefore preferably a martensitic or at least partially martensitic structure, since this has a particularly high hardness.
  • the steel substrate is a steel which, in addition to iron and unavoidable impurities (in wt. %), consists of
  • V ⁇ 0.1 wt.%.
  • the elements P, S, N, Sn, As, Ca are impurities that cannot be completely avoided during steel production. In addition to these elements, other elements may also be present in the steel as impurities. These other elements that may be present in the steel as impurities in addition to the elements P, S, N, Sn, As, Ca are summarized under "unavoidable impurities".
  • the total content of unavoidable impurities is preferably a maximum of 0.2% by weight, preferably a maximum of 0.1% by weight.
  • the optional alloying elements Cr, B, Nb, Ti, for which a lower limit is specified, can also occur in the steel substrate as unavoidable impurities in contents below the respective lower limit.
  • the C content of the steel is a maximum of 0.37 wt.% and/or at least 0.06 wt.%. In particularly preferred embodiments, the C content is in the range of 0.06 - 0.09 wt.% or in the range of 0.12 - 0.25 wt.% or in the range of 0.33 - 0.37 wt.%.
  • the Si content of the steel is a maximum of 1.00 wt.% and/or at least 0.06 wt.%.
  • the Mn content of the steel is a maximum of 2.4 wt.% and/or at least 0.75 wt.%. In particularly preferred variants, the Mn content is in the range of 0.75 - 0.85 wt.% or in the range of 1.0 - 1.6 wt.%.
  • the Al content of the steel is a maximum of 0.75% by weight, in particular a maximum of 0.5% by weight, preferably a maximum of 0.25% by weight. Alternatively or additionally, the Al content is preferably at least 0.02%.
  • the sum of the contents of silicon and aluminum is limited.
  • the sum of the contents of Si and Al (usually referred to as Si+Al) is therefore a maximum of 1.5 wt.%, preferably a maximum of 1.2 wt.%.
  • the sum of the contents of Si and Al is at least 0.06 wt.%, preferably at least 0.08 wt.%.
  • the elements P, S and N are typical impurities that cannot be completely avoided during steel production.
  • the P content is a maximum of 0.03% by weight.
  • the S content is preferably a maximum of 0.012%.
  • the N content is preferably a maximum of 0.009% by weight.
  • the steel also contains chromium with a content of 0.08 - 1.0 wt.%.
  • the Cr content is preferably a maximum of 0.75 wt.%, in particular a maximum of 0.5 wt.%.
  • the sum of the contents of chromium and manganese is preferably limited.
  • the sum is a maximum of 3.3% by weight, in particular a maximum of 3.15% by weight.
  • the sum is at least 0.5% by weight, preferably at least 0.75% by weight.
  • the steel optionally also contains boron with a content of 0.001 - 0.005 wt.%.
  • the B content is a maximum of 0.004 wt.%.
  • the steel may contain molybdenum in a content of not more than 0.5% by weight, in particular not more than 0.1% by weight.
  • the steel can optionally contain nickel with a content of maximum 0.5 wt.%, preferably maximum 0.15 wt.%.
  • the steel may also contain copper with a maximum content of 0.2 wt.%, preferably a maximum of 0.15 wt.%.
  • the steel can optionally contain one or more of the microalloying elements Nb, Ti and V.
  • the optional Nb content is at least 0.02 wt.% and a maximum of 0.08 wt.%, preferably a maximum of 0.04 wt.%.
  • the optional Ti content is at least 0.01 wt.% and a maximum of 0.08 wt.%, preferably a maximum of 0.04 wt.%.
  • the optional V content is a maximum of 0.1 wt.%, preferably a maximum of 0.05 wt.%.
  • the sum of the contents of Nb, Ti and V is preferably limited.
  • the sum is a maximum of 0.1 wt.%, in particular a maximum of 0.068 wt.%. Furthermore, the sum is preferably at least 0.015 wt.%.
  • the invention further relates to a method for producing a flat steel product according to the invention comprising at least the following work steps: a) providing a flat steel product comprising a steel substrate consisting of a steel containing 0.1 - 3 wt.% Mn and optionally up to 0.01 wt.% B, and an aluminum-based anti-corrosion coating applied to the steel substrate, b) applying an absorption layer comprising carbon particles to the flat steel product, in particular by
  • the aqueous dispersion with carbon particles is evenly distributed over the entire surface, so that a homogeneous, surface-covering absorption layer comprising carbon particles is formed.
  • the homogeneous, area-covering absorption layer is formed by chemical or physical vapor deposition.
  • the pH value of the aqueous dispersion is a maximum of 14, in particular a maximum of 13, preferably a maximum of 12, particularly preferably a maximum of 10. This ensures that the aluminum-based anti-corrosive coating is well wettable and thus that the aqueous dispersion and the carbon particles contained therein are distributed particularly evenly. It has proven to be particularly practical if the pH value of the aqueous dispersion is at least 8 and a maximum of 12, in particular at least 8 and a maximum of 10.
  • the aqueous dispersion contains 1 - 70 wt.%, in particular 2 - 50 wt.% carbon particles based on the total weight of the aqueous dispersion.
  • the aqueous dispersion additionally contains at least one surfactant.
  • This can improve the stability the dispersion can be improved.
  • the presence of at least one surfactant in the aqueous dispersion also has a beneficial effect on the wettability of the aluminum-based anti-corrosion coating.
  • the proportion of at least one surfactant in the aqueous dispersion is 0 to 5% by weight based on the total weight of the aqueous dispersion.
  • a minimum content of 0.1% by weight is required to obtain the advantageous effects mentioned.
  • the addition of more than 5% by weight is not sensible for economic reasons, since an increase in the advantageous effects can no longer be observed.
  • the proportion of the at least one polymer in the aqueous dispersion is 0 to 50% by weight based on the total weight of the aqueous dispersion. A minimum content of 1% by weight is required to obtain the advantageous effects mentioned. The addition of more than 50% by weight has a detrimental effect on the degree of reflection and the drying of the absorption layer obtained from the aqueous dispersion.
  • the proportion of carbon particles and the proportion of the optionally present at least one surfactant and the optionally additionally present at least one polymer in the aqueous dispersion can be varied depending on the type of application in order to set a desired proportion of the carbon particles and the optionally present at least one surfactant and the optionally additionally present at least one polymer in the dry absorption layer.
  • aqueous dispersion with a significantly lower proportion of carbon particles for immersion whereas for coating a higher proportion of carbon particles in the aqueous dispersion is required in order to obtain the same desired proportion of carbon particles in the dry absorption layer.
  • the immersion is preferably carried out for an immersion time of 0.5 to 30 s, preferably 1 to 5 s.
  • a longer immersion time has the advantage that the wetting of the flat steel product is ensured.
  • a shorter immersion time is advantageous in order to make the production process efficient. The times mentioned have proven to be a good compromise in this respect.
  • the flat steel product has a temperature of 40°C to 100°C, preferably 50°C to 80°C, when the aqueous dispersion is applied, in particular when dipping or spraying or coating in the coil coating process or when coating by chemical vapor deposition.
  • a higher temperature accelerates the drying of the absorption layer and thus the layer formation; however, if the temperature is too high, the aqueous dispersion evaporates too quickly, so that the layer formation is not reliably completed.
  • the temperature ranges mentioned are advantageous for chemical vapor deposition in order to accelerate the reactions on the surface.
  • the coating can be carried out in such a way that, for example, the combustion of gas, for example methane, propane, butane or acetylene, takes place on a hot flat steel product surface which is formed by the aluminum-based anti-corrosion coating, or the coating takes place via a liquid-supply flame spray pyrolysis in which a carbon containing precursor, for example methane, propane, butane or acetylene, is incompletely burned and the carbon particles produced thereby adhere to the surface of the flat steel product or the coating is carried out from a carbon target, for example graphite or amorphous carbon, by a sputtering PVD process in a vacuum.
  • a carbon target for example graphite or amorphous carbon
  • the flat steel product is subjected to an activation treatment before step b), whereby an adhesion promoter is applied to the aluminum-based anti-corrosion coating.
  • an adhesion promoter is applied to the aluminum-based anti-corrosion coating.
  • the same polymers that have already been described in detail above with regard to the flat steel product according to the invention can serve as adhesion promoters.
  • the configurations of these polymers described there can be applied analogously to the method according to the invention.
  • the invention further relates to a method for producing a sheet metal part comprising the following work steps: a) providing a sheet metal blank from a flat steel product according to the invention; b) heating the sheet metal blank in such a way that the AC3 temperature of the blank is at least partially exceeded and the temperature TEinig of the blank when placed in a forming tool intended for hot press forming (work step c)) at least partially has a temperature above Ms+100°C, where Ms denotes the martensite start temperature, the average heating rate being greater than 15 Kmm/s; c) placing the heated sheet metal blank in a forming tool, the time required for removing it from the heating device and placing the the transfer time trrans required for the blank is at most 20 s, preferably at most 15 s; d) hot-press forming the sheet metal blank to form the sheet metal part, wherein the blank is cooled during the hot-press forming over a period twz of more than 1 s at a cooling rate rwz
  • a blank which consists of a previously explained flat steel product according to the invention (work step a)). This is heated at an average heating rate of more than 15 Kmm/s in such a way that the AC3 temperature of the blank is at least partially exceeded and the temperature TEinig of the blank when placed in a forming tool intended for hot press forming (work step c)) is at least partially above Ms+100°C.
  • the average heating rate is the product of the average heating speed from 30°C to 700°C and the sheet thickness.
  • the average heating rate is more than 15 Kmm/s, in particular more than 20 Kmm/s, preferably more than 25 Kmm/s, in particular more than 30 Kmm/s.
  • the heating in step a) preferably takes place in a furnace, in particular a roller hearth furnace. Therefore, heat radiation dominates over heat conduction when heating the sheet metal blanks.
  • the absorption layer according to the invention increases the proportion of absorbed heat radiation, resulting in the advantageous high average heating rates.
  • partially exceeding a temperature means that at least 30%, in particular at least 60%, of the volume of the blank has a corresponding temperature exceed.
  • at least 30% of the blank has an austenitic structure, i.e. the transformation from a ferritic to an austenitic structure does not have to be complete when placed in the forming tool.
  • up to 70% of the volume of the blank when placed in the forming tool can consist of other structural components, such as tempered bainite, tempered martensite and/or non- or partially recrystallized ferrite.
  • certain areas of the blank can be kept at a lower temperature than others during heating.
  • the heat supply can be directed only at certain sections of the blank, or the parts that are to be heated less can be shielded from the heat supply.
  • the part of the blank material whose temperature remains lower no or only significantly less martensite is formed during forming in the tool, so that the structure there is significantly softer than in the other parts that have a martensitic structure.
  • a softer area can be specifically set in the respective formed sheet metal part, for example by providing an optimal toughness for the respective intended use, while the other areas of the sheet metal part have a maximized strength.
  • Maximum strength properties of the resulting sheet metal part can be achieved by ensuring that the temperature reached at least partially in the sheet metal blank is between AC3 and 1000°C, preferably between 850°C and 950°C.
  • the minimum temperature AC 3 to be exceeded is determined according to the formula given by HOUGARDY, HP. in Maschinenstoff ambience Stahl Volume 1: Kunststoff, Verlag Stahleisen GmbH, Düsseldorf, 1984, p. 229.
  • An optimally uniform distribution of properties can be achieved by completely heating the blank in step b).
  • the heating takes place in an oven with an oven temperature Tofen of at least 850°C, preferably at least 880°C, particularly preferably at least 900°C, in particular at least 920°C, and at most 1000°C, preferably at most 950°C, particularly preferably at most 930°C.
  • an oven temperature Tofen of at least 850°C, preferably at least 880°C, particularly preferably at least 900°C, in particular at least 920°C, and at most 1000°C, preferably at most 950°C, particularly preferably at most 930°C.
  • the dew point in the oven is at least -20°C, preferably at least -15°C, in particular at least -5°C, preferably at least 0°C, particularly preferably at least +5°C and at most +25°C, preferably at most +20°C, in particular at most +15°C.
  • the heating in step b) takes place step by step in areas with different temperatures.
  • the heating takes place in a roller hearth furnace with different heating zones.
  • the heating takes place in a first heating zone with a temperature (so-called furnace inlet temperature) of at least 650°C, preferably at least 680°C, in particular at least 720°C.
  • the maximum temperature in the first heating zone is preferably 900°C, in particular a maximum of 850°C.
  • the maximum temperature of all heating zones in the furnace is preferably a maximum of 1200°C, in particular a maximum of 1000°C, preferably a maximum of 950°C, particularly preferably a maximum of 930°C.
  • the total time in the oven which consists of a heating time and a holding time, is preferably at least 1 minute for both variants (constant oven temperature, gradual heating), in particular at least 2 minutes, preferably at least 3 minutes. Furthermore, the total time in the furnace for both variants is preferably a maximum of 12 minutes, in particular a maximum of 10 minutes, preferably a maximum of 8 minutes, in particular a maximum of 6 minutes. Longer total times in the furnace have the advantage that uniform austenitization of the sheet metal blank is ensured. On the other hand, holding for too long above AC3 leads to grain coarsening, which has a negative effect on the mechanical properties.
  • the blank heated in this way is removed from the respective heating device and transported into the forming tool so quickly that its temperature when it arrives in the tool is at least partially above Ms+100°C, preferably above 600°C, in particular above 650°C, particularly preferably above 700°C.
  • Ms refers to the martensite start temperature.
  • the temperature is at least partially above the ACl temperature.
  • the temperature is in particular a maximum of 900°C.
  • step c) the transfer of the austenitized blank from the heating device used to the forming tool is completed preferably within a maximum of 20 seconds, in particular within a maximum of 15 seconds. Such rapid transport is necessary to avoid excessive cooling before deformation.
  • the tool When the blank is inserted, the tool typically has a temperature between room temperature (RT) and 200°C, preferably between 20°C and 180°C, in particular between 50°C and 150°C.
  • the tool can be tempered at least in some areas to a temperature Twz of at least 200°C, in particular at least 300°C, in order to only partially harden the component.
  • the tool temperature Twz is preferably maximum 600°C, in particular maximum 550°C. It is only necessary to ensure that the tool temperature Twz is below the desired target temperature Tziei.
  • the residence time in the tool twz is preferably at least 2s, in particular at least 3s, particularly preferably at least 5s.
  • the maximum residence time in the tool is preferably 25s, in particular a maximum of 20s.
  • the target temperature Tziei of the sheet metal part is at least partially below 400°C, preferably below 300°C, in particular below 250°C, preferably below 200°C, particularly preferably below 180°C, in particular below 150°C.
  • the target temperature Tziei of the sheet metal part is particularly preferably below Ms-50°C, where Ms denotes the martensite start temperature.
  • the target temperature of the sheet metal part is preferably at least 20°C, particularly preferably at least 50°C.
  • the martensite start temperature of a steel within the scope of the inventive specifications is according to the formula:
  • Ms [°C] (490.85 - 302.6 %C - 30.6 %Mn - 16.6 %Ni - 8.9 %Cr + 2.4 %Mo - 11.3%Cu + 8.58 %Co + 7.4 %W - 14.5 %Si) [°C/wt.%], where C% is the C content, %Mn is the Mn content, %Mo is the Mo content, %Cr is the Cr content, %Ni is the Ni content, %Cu is the Cu content, %Co is the Co content, %W is the W content and %Si is the Si content of the respective steel in wt.%.
  • AC1[°C] (739 — 22*%C - 7*%Mn + 2*%Si + 14*%Cr + 13*%Mo - 13*%Ni +20*%V )[°C/wt.%]
  • AC3[°C] (902 - 225*%C + 19*%Si - ll*%Mn - 5*%Cr + 13*%Mo - 20*%Ni +55*%V)[°C/wt.%], where %C is the C content, %Si is the Si content, %Mn is the Mn content, %Cr is the Cr content, %Mo is the Mo content, %Ni is the Ni content and +%V is the vanadium content of the respective steel (Brandis H 1975 TEW-Techn. Ber. 1 8-10).
  • the blank is not only formed into the sheet metal part, but is also quenched to the target temperature at the same time.
  • the cooling rate in the tool rwz to the target temperature is in particular at least 20 K/s, preferably at least 30 K/s, in particular at least 50 K/s, particularly preferably at least 100 K/s.
  • the sheet metal part After removal of the sheet metal part in step e), the sheet metal part is cooled to a cooling temperature TAB of less than 50°C within a cooling time tAB of 0.5 to 600 s. This is usually done by air cooling.
  • Figure 3 Reflectance as a function of the application weight of the absorption layer;
  • Figure 4 Heating rate as a function of the application weight of the absorption layer.
  • examples 1 to 7 according to the invention and a comparative example V were carried out.
  • steel blanks measuring 100 x 200 mm with a thickness of 1.5 mm and having a steel composition according to Table 1 were coated with an aluminum-based anti-corrosion coating by means of hot-dip coating.
  • the melt analysis of the anti-corrosive coating is shown in Table 2.
  • the resulting anti-corrosive coating had an Al base layer whose composition corresponded to the melt analysis.
  • the one-sided thickness of the anti-corrosive coating was 25 pm.
  • the steel blanks thus prepared were treated with an aqueous dispersion comprising carbon particles in order to produce an absorption layer on the anti-corrosive coating (inventive examples 1 to 7).
  • the respective composition of the aqueous dispersion can be found in Table 3.
  • Table 3 also contains details of the treatment method. These include the application method, the pH value of the aqueous dispersion, the immersion time and the temperature of the steel blanks during treatment.
  • the resulting properties such as the coating weight of the absorption layer and the layer thickness of the absorption layer after drying, the average reflectance in the infrared range and the heating rate, are also listed in Table 3.
  • inventive examples 1 to 7 have significantly lower average reflectances in the infrared range compared to comparative example V (see also Figure 3). Furthermore, the heating rate for the inventive examples 1 to 7 is significantly higher than for comparative example V (see - ZI - also Figure 4).
  • the average degree of reflection decreases with increasing application weight or increasing layer thickness of the dry absorption layer, considered for the use of an aqueous dispersion with the same proportion of carbon particles, while the heating rate increases accordingly (see comparison of examples 3 to 7 according to the invention).
  • a comparison of examples 6 and 7 according to the invention shows that from a certain application weight or from a certain layer thickness of the absorption layer, saturation of the effect according to the invention occurs (see also Figures 3 and 4).
  • the steel blanks produced in this way were then processed into a sheet metal part by hot forming.
  • the blanks were heated in a roller hearth furnace from room temperature with an average heating rate (between 30°C and 700°C) to an oven temperature of 920°C.
  • the average heating rate is given in Table 3.
  • the blanks were then processed in a conventional manner.
  • the blanks were removed from the roller hearth furnace and placed in a forming tool. When removed from the furnace, the blanks had reached the furnace temperature.
  • the transfer time which consists of the removal from the heating device, transport to the tool and insertion into the tool, was approximately 10 s.
  • the temperature of the blanks when placed in the forming tool was in all cases above the respective ACl temperature and thus also above Ms+100°C.
  • Remainder iron and unavoidable impurities Values in % by weight.

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Abstract

L'invention se rapporte à un produit plat en acier permettant de produire une pièce en acier par formage à chaud, comprenant un substrat en acier, qui est constitué d'un acier présentant 0,1 à 3 % en poids de Mn et éventuellement jusqu'à 0,01 % en poids de B, et un revêtement anticorrosion à base d'aluminium déposé sur le substrat en acier, une couche d'absorption comprenant des particules de carbone étant agencée sur le revêtement anticorrosion. L'invention se rapporte en outre à un procédé permettant de produire un produit plat en acier selon l'invention et à l'utilisation de particules de carbone dans une couche d'absorption sur un produit plat en acier revêtu d'un revêtement anticorrosion à base d'aluminium, afin de réduire la réflectivité dans le domaine infrarouge. L'invention se rapporte également à un procédé permettant de produire une pièce de tôle à partir d'un produit plat en acier selon l'invention.
PCT/EP2023/079226 2022-10-20 2023-10-20 Produit plat en acier permettant de produire une pièce en acier par formage à chaud, son procédé de production et procédé de production de pièce en acier WO2024084018A1 (fr)

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Citations (7)

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JP2008195999A (ja) * 2007-02-13 2008-08-28 Jfe Steel Kk ホットプレス用鋼板およびその製造方法
JP2009286092A (ja) * 2008-06-02 2009-12-10 Nippon Steel Corp 機器筐体
JP2011149084A (ja) * 2010-01-25 2011-08-04 Nippon Steel Corp 昇温特性に優れた熱間プレス用Ａｌめっき鋼板及びその製造方法
WO2012120081A2 (fr) 2011-03-08 2012-09-13 Thyssenkrupp Steel Europe Ag Produit plat en acier et procédé de fabrication d'un produit plat en acier
US20120328871A1 (en) * 2010-02-19 2012-12-27 Tapan Kumar Rout Strip, Sheet or Blank Suitable for Hot Forming and Process for the Production Thereof
US20170268078A1 (en) * 2014-03-31 2017-09-21 Arcelormittal Method of producing press-hardened and coated steel parts at a high productivity rate
WO2022215229A1 (fr) * 2021-04-08 2022-10-13 日本製鉄株式会社 Feuille d'acier pour estampage à chaud et élément estampé à chaud

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JP2008195999A (ja) * 2007-02-13 2008-08-28 Jfe Steel Kk ホットプレス用鋼板およびその製造方法
JP2009286092A (ja) * 2008-06-02 2009-12-10 Nippon Steel Corp 機器筐体
JP2011149084A (ja) * 2010-01-25 2011-08-04 Nippon Steel Corp 昇温特性に優れた熱間プレス用Ａｌめっき鋼板及びその製造方法
US20120328871A1 (en) * 2010-02-19 2012-12-27 Tapan Kumar Rout Strip, Sheet or Blank Suitable for Hot Forming and Process for the Production Thereof
WO2012120081A2 (fr) 2011-03-08 2012-09-13 Thyssenkrupp Steel Europe Ag Produit plat en acier et procédé de fabrication d'un produit plat en acier
EP2683843B1 (fr) * 2011-03-08 2021-06-16 ThyssenKrupp Steel Europe AG Produit plat en acier et procédé de fabrication d'un produit plat en acier
US20170268078A1 (en) * 2014-03-31 2017-09-21 Arcelormittal Method of producing press-hardened and coated steel parts at a high productivity rate
WO2022215229A1 (fr) * 2021-04-08 2022-10-13 日本製鉄株式会社 Feuille d'acier pour estampage à chaud et élément estampé à chaud

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